1. Field of the Invention
This invention relates to solid acid catalysts in general. More specifically, this invention is concerned with strong solid acid catalysts suitable to catalyze isoparaffin-olefin alkylation reactions.
2. Description of the Prior Art
A comprehensive text on solid acids and bases was written by Kay Tanabe, et al., entitled New Solid Acids and Bases Their Catalytic Properties. In this book there is a section beginning on page 199 entitled Super Acids. Discussed in this section were solid acids comprising sulfated oxides of titanium, zirconium, or iron. The use of such compounds is well-known for purposes of acid catalyzed reactions, such as alkylation and cracking. They were found to have higher acid catalyzing properties than sulfuric acid alone. Not discussed or disclosed in this section was the use of mixed oxides; e.g., binary oxides, of super acids to further enhance acid catalyzing properties. No additional metal oxide species in combination with sulfated oxides of titanium, zirconium, or iron to further enhance their catalytic properties are either disclosed or suggest. A direct comparison of a zirconium oxide promoted with sulfate as contrasted to a titanium oxide promoted with sulfate, with no other factors involved, zirconium uniformly has superior super acid properties.
Alternatively, trying to promote zirconium oxides with additional materials other than sulfate to enhance their acid properties as demonstrated in an example in this case, have uniformly been found not to yield superior acidic properties. In other words, a nickel oxide zirconium mixed oxide matrix promoted by sulfate does not lead to an enhanced solid acid having properties superior to the zirconium oxide without the nickel promotion. In an example of this Specification, mixed nickel and zirconium oxide matrices having nickel in concentration range 0.1 to 3.3 wt % were tried and promoted with sulfate concentrations in the range 2.0 to 4.2 wt %. The results are reported in a table and an associated graph.
Other methods of promoting solid acidity that appear in the literature have to do with the addition of a platinum metal to a super acid oxide. The platinum apparently is not an oxide, but is functioning like a hydrogenation transfer agent. Platinum is known to cause the homolytic scission of hydrogen to hydrogen bonds. Its presence in a strong solid acid has been hypothesized to encourage ionic scission of hydrogen to hydrogen bonds, i.e. to form H+ and H- type species. There is nothing in the promotion of solid oxides by the presence of platinum that suggests that the platinum is in the form of an oxide or functions through an oxide structure. Some improvement has been reported as a result of the addition of platinum as a platinum metal. This is to be distinguished from the advantages disclosed in the instant invention for an oxide of a Group VIII metal.
In an article entitled Effect of Acid Strength on the Catalytic Activity of NiO-TiO.sub.2 Modified with Acids of J. R. Sohn, et al., published in JOURNAL OF CATALYSIS, 127,449-452 (1991), the co-precipitation of nickel hydroxide and titanium hydroxide by adding ammonium hydroxide slowly to a mixed solution of nickel chloride, titanium chloride, and hydrochloric acid at room temperature produced a precipitated material, which after thorough washing to remove chloride, was dried at room temperature for 12 hours. Other methods of drying the chloride-free precipitate, indicate an evacuated chamber at a temperature of 400.degree. C. for 1.5 hours in contrast to the 12 hours. The catalyst was used for purposes of isomerization of 1-butene. No other catalytic reactions were suggested or disclosed. A nickel oxide content was reported to be 25 mole % in the only example showing the isomerization properties of the catalyst. Mention of a catalyst being prepared having a nickel oxide content of 4 mole % was also made. However, the 4 mole % was used to keep the content of nickel down so that Hammett Indicators could be used. Hammett Indicators give rise as was explained in the article to color changes dependent upon the acid strength of the catalyst. However, if the catalyst itself were colored, this tended to mask any color changes that would otherwise be observable by means of Hammett Indicators. Consequently, the low concentration of nickel oxide was not due to any attempt to maximize or explore lower concentrations of nickel for purposes of catalyzing isomerization reactions but rather only to be able to better determine color changes of certain Hammett Indicators.
The instant invention distinguishes over the materials disclosed in this Journal of Catalysis article because the nickel content of their isomerization catalyst was far outside of any range suitable for the instant invention. In fact, it has been found that increasing weight percent or mole percent of nickel leads to a progressive decrease in alkylation activity. Not disclosed in this article is the criticality of nickel oxide content nor the use of the catalyst for purposes other than isomerization.
In U.S. Pat. No. 5,036,035 (issued Jul. 30, 1991) entitled Solid, Strong Acid Catalyst Process for the Production of the Same and Use Thereof, a solid strong acid catalyst useful for hydrocarbon reactions, specifically skeletal isomerization, is disclosed wherein supported sulfate ions in the presence of Group III, Group IV, and Group VIII metals are disclosed. The Group VIII metals include nickel, platinum, ruthenium, rhodium, palladium, osmium, and uranium. The Group III metals include aluminum, gallium, indium, and thallium. The Group IV metals include titanium, zirconium, silicon, germanium, and tin. Longer catalyst life of the sulfated oxide was discovered to result from the presence of Group VIII metals and sulfate. Essentially, a Group VIII metal was added to a support of hydroxides or oxides of Group IV and/or Group III metals. The only instance of co-precipitation disclosed anywhere in the specification consisted of the preparation of a Group III and Group IV metals together to form the support. In no instance is there an example of the co-precipitation of titanium, a Group IV metal, and nickel, a Group VIII metal. The incorporation of a Group VIII metal was disclosed to be either before, after, or simultaneous with sulfation. There is reported to be a benefit from first sulfating by treating with a metal-free sulfate-containing agent and then introducing the Group VIII metals thereon. Also reported is the fact that it is important to effect calcining and stabilizing treatment at a temperature of 450.degree. to 800.degree. C. Lower temperatures are suggested as possible, but not preferred. Perhaps the higher temperature calcination is preferred in the case of sequential precipitation in contrast to the instant invention that prefers temperatures of calcination not exceeding 450.degree. C. for a mixed oxide. A mixed oxide is a unique material that results from co-precipitated hydroxides of nickel and titanium. Not disclosed are the dual limitations of nickel oxide content, which is not significantly higher than 4% by weight, and a calcination temperature not exceeding 450.degree. C. In summary, there is no teaching in which a Group VIII and a Group IV or Group III oxide or hydroxide are co-precipitated to form a solid which is subsequently sulfated, nor is the content of nickel or the calcination temperature taught to be critical.
For a comprehensive background in alkylation reactions that are relevant to this invention, see Industrial and Laboratory Alkylation, vol. 5 (1977) of the American Chemical Society Symposium Series, edited by L. S. Albright and A. R. Goldsby. Other references of relevance are: U.S. Pat. No. 5,120,897 to Del Rossi, et al. (Jun. 9. 1992); U.S. Pat. No. 4,956,518 to Child et al. (Sep. 11, 1990); U.S. Pat. No. 4,967,034 to Miller et al. (Oct. 30, 1990); U.S. Pat. No. 4,918,255 to Chou et al. (Apr. 17, 1990); U.S. Pat. No. 5,012,033 to Child et al. (Apr. 30, 1991); and U.S. Pat. No. 4,384,161 to Huang et al. (May 17, 1983). Adamantane has been disclosed in U.S. Pat. No. 5,157,199 to Soled et al. (Oct. 20, 1992) to catalyze isomerization.